1. Field of the Invention
This invention relates to the handling of stacks of sheet material and particularly to the supplying of or removal of stacks of paper from reproduction equipment to enable continuous running.
2. Description of the Related Art
Xerographic reproduction equipment is utilized in a wide variety of environments including relatively low volume office use to substantially higher volume contract reproduction uses. For lower volume uses, insertable trays and slidable drawers comprise effective means for holding supplies of sheets of paper on which copies are made. For high volume reproduction operations, users require large paper supply sources for maximization of machine running time which, correspondingly, requires a minimization of machine down time for such operations as reloading paper and unloading copies. For these reasons, it has become necessary to develop large capacity sheet feeding systems which allow continuous operation so that there is substantially no hiatus in the reproduction operation as the supply of sheets from one supply is exhausted and replaced with sheets from another supply. These systems further require the capability of loading additional stacks of paper while the machine continues to run. Similar considerations apply to equipment for unloading finished copies from such reproduction equipment.
In addition to fulfilling the above-described technical requirements, these systems are under cost and size constraints. Because the number of high volume machines sold is relatively low, in comparison to office size equipment, more simple designs help to prevent costs from being excessively high, as the cost must be amortized over a smaller number of units likely to be sold. In addition, space efficient designs minimize the floor space required for the equipment, which is a critical factor in metropolitan areas where floor space costs are high.
One arrangement for increasing paper supply in low volume desk top copiers is shown in U.S. Pat. No. 4,525,063. This design uses a double sided paper supply tray. When one side of the tray is exhausted, the user merely removes the tray and reinserts the other side of the tray into the machine. Such an arrangement is not suitable for high volume applications because of low capacity and the operator intervention required to switch the tray.
For higher volume operations, machines having large capacity supply trays, or multiple supply trays with means for switching from an empty tray to a full tray have been proposed. U.S. Pat. Nos. 3,415,510, 4,008,957 and 4,484,734 illustrate such systems. In general, the design of such systems and the controls for such systems are relatively more complex, take up more space, and are costly.
One design for providing stacks of sheets for high volume operation is shown in U.S. Pat. No. 4,153,242. This design utilizes two rolling carriages, one placed above the other with elevators for lifting carriages from their tracks to a feed position. Such an arrangement requires a costly elevator system for raising and lowering the carriages.
Other systems, such as shown in U.S. Pat. Nos. 3,975,011 and 4,174,831 employ a bottom feeding arrangement wherein a temporary holding means holds a portion of the stack in a feed position, while additional sheets are elevated into position from beneath. Thereafter, the temporary support means is removed and the supply stack is held in position by the stack elevator. Such systems require the temporary holding means which increases cost and space required for the feeder.
U.S. Pat. No. 4,418,907 shows a laterally movable stack tray. However, this design requires a stack elevator with increased vertical movement to pass upwardly beyond the sheet feeding rolls to add a stack of sheets from a resupply tray.